Infra-red detection apparatus



Nov. 27, 1962 R. M. POORMAN ET AL 3,066,222

INFRA-RED DETECTION APPARATUS Filed Nov. 18, 1959 r v I r x I v r u I I:

GEORGE c. HAETTINGER ROBERT F. OCONNELL A T TORNE Y proper operatingtemperature conditions.

3,066,222 NRA-RED DETECTION APPARATUS Richard M. Poorman, George C.Haettinger, and Robert F. UConneil, indianapohs, Ind, assignors to UnionCarbide Corporation, a corporation of New York Filed Nov. 18, 1959, Ser.No. 853,737 9 Claims. (1. 25033.3}

This invention relates to an improved refrigerated mounting means for aninfrared detection cell utilizing cryogenic liquids. More particularlyit relates to such a means having improved filling and venting means forthe refrigerant liquids.

Infra-red sensing apparatus is quite useful for detecting the locationof objects by the infra-red or heat waves radiating from the object.certain air-to-air missiles, for example, is operated by means of such asensing apparatus. It has been found that the infra-red detection cellis most effective when maintained at an extremely low temperature, suchas the temperature of liquid nitrogen, hydrogen or helium. Therefore aconsiderable effort has been expended by the industry to produceapparatus which effectively cools an infra-red sensing element to suchlow temperatures and which also does not use prohibitive amounts of theliquid refrigerant.

In such apparatus weight and size are very critical factors, hence it isof paramount importance to achieve maximum efficiency in therefrigeration system so that a minimum of refrigerant will be necessaryto maintain Previously available apparatus has utilized rather crudefilling and venting means in the form of a filler hole in the top of thecontainer with a vented stopper therefor. This crude filling and ventingsystem permits considerable heat leak into the refrigerant storagecontainer with attendant vaporization and loss of refrigerant. Whenwork'ng with refrigerants, like liquid nitrogen, where temperaturesapproach absolute zero even such small paths for heat transfer causevery great difficulty.

It is accordingly a primary object of this invention to provide arefrigerated mounting means for an infra-red detection cell havingimproved thermal efficiency.

It is a further object to provide such an apparatus having improvedfilling and venting means.

Other objects and advantages will be apparent from the description anddrawings in which:

FIG. 1 is a cross-sectional view of a preferred embodiment ofrefrigerated mounting means for an infrared detection cell according tothe invention,

FIG. 2 is a cross-sectional view of another embodiment of the inventionand FIG. 3 is a cross-sectional view of still another embodiment of theinvention.

The objects of the invention are accomplished in general by a novel unitwhich stores low temperature refrig erant and supplies refrigeration toinfra-red detection cell and which has improved filling and ventingmeans. The apparatus consists of inner and outer vessels forming adouble-walled container employing vacuum space insulation and preferablyopacified-vacuum insulation between the walls. An insulateddouble-walled tube extends inward from an outer wall of the containerinto the inner vessel and terminates near the opposite wall of the innervessel. A removable filling line for liquid refrigerant can e readilyinserted into the tube for charging the inner vessel. Vapors from therefrigerant are vented out through the tube around the filling line. Ina preferred modification of the present invention, the combinationfilling and vent tube is positioned at the bottom of t e container, andan extension projects from the side of the container to provide a meansfor mounting the infrared The homing mechanism on States atent' icedetection device and also to provide a means of keeping it cold.

The invention will now be described in more detail with respect to theaccompanying figures. In the embodiment of FIG. 1 the container lil isformed from an inner vessel 12 and an outer vessel 14, both preferablyconstructed of brass, aluminum, or aluminum alloys. The space betweenthe vessels is under a vacuum pressure and preferably contains' anopacified insulating jacket 16 and gas adsorbent material 18communicating with the opacified insulation to maintain the space undera vacuum.

Inner concentric extension tubes 20 and 22 of inner vessel 12 and outervessel 14 respectively are joined at point 24 to form a double-walledinsulated tube extending inward from one wall of the container to apoint adjacent the opposite wall of the inner vessel. A filling line 26is inserted through this tube to charge the inner vessel with liquidrefrigerant, such as liquid nitrogen. The filling line 26 is designed todischarge the refrigerant at an angle so that the refrigerant does notflow back down through the bottom filling and vent tube. Vapors from therefrigerant can be vented out through the filling and vent tube aroundthe filling line 26. Once the inner vessel has received a desired amountof refrigerant, the filling line is withdrawn and a stopper (not shown)is placed into the outlet 28 of the filling tube. This further reducesheat inleak along the filling and vent tube. This stopper will have avent opening to allow the escape of vapors from the inner vessel. Aporous plug might also be used. The particular filling and vent means ofthis invention has the unique advantage of allowing the use of a longcombination fill and vent tube without extending the overall dimensionsof the container. The relatively long insulated filling tube provides ahigh resistance to heat flow from the outer vessel to the inner vessel.Also, part of the refrigeration in the vapors leaving the container canbe recovered by heat exchange along the walls of the filling tube.

The double-walled filling and vent tube is so located within thecontainer that when the container is in its normal position, no liquidrefrigerant will be present within the opening. Thus, under pressure dueto vaporization build-up within the container, the liquid refrigerantwill not be forced out through the filling and vent tube. Positioningthis combination tube in the bottom or sides of the containeraccomplishes this result.

It should be noted that the particular improved filling and vent tubeand its combination with a filling line described herein is not limitedto use with infrared detection cell cooling systems. These improvementsare quite useful for other cryogenic apparatus wherein size of thecontainer must be minimized and a desirably long filling tube heat pathis required. Such improvement is especially useful for containers havingstorage capacity less than about 50 liters.

An extension 39 located on the side of container 10 provides a means formounting an infra-red detection cell 32 and a means for keeping the cellcold. This extension consists of a solid rod 34 of material having highthermal conductivity and low coefficient of thermal expansion, such assapphire. It is positioned in thermal contact with inner vessel 12 andis supported as a cantilever beam by ring 36 attached to or a part ofinner vessel 12. Infrared detection cell 32 is mounted in thermalcontact with the unsupported end of rod 34. This rod 34 is surrounded byextension 38 of outer vessel 14 to enable this portion of the containerto have vacuum type insulation. Mounting the infra-red detection cell 32in an evacuated space prevents it from being hampered in its operationby frost accumulation which could occur if it were exposed directly tothe atmosphere. Also the refrigeration loss is reduced. The use of solidrod 34 to conduct refrigeration to the detection cell has the additionaladvantage of reducing the noise level in the detection circuit. Suchhigh noise level caused by boiling liquid was undesirably present inprior art systems wherein the liquid refrigerant was positioned near thecell. A window 40 fabricated from sapphire, for example, is positionedin the end of extension 58 to form an area of high infrared transmissionto enable the detection cell to operate at maximum efficiency.Electrical connection 42 to cell '32 can be introduced to the vacuumspace at any convenient position. When any opacified material isemployed in the evacuated insulation space to increase insutatieneflicien'cy, it is understood that this material should not bepositioned between the detection cell and the transmission window. Thiscan be achieved in several convenient fashions. For example, if a foiland fiber glass wrapped insulation combination is employed in theevacuated space, the foil and fibers are terminated before blocking thewindow.

It has been found that the distance between the cell 32 and the end ofextension 38 is quite critical in order to satisfy the opticalrequirements of the system. In order to maintain this distance asconstant as possible, the inner vessel 12 is supported at one end by ahollow plastic spacing member 44 positioned between inner vessel 12 andextension 38 of outer vessel 14 and attached to both vessels 12 and 14by adhesive. Member 44 should have a thermal coefficient of expansionsimilar to that of rod 30. In this manner when rod 30 contracts 'due tocooling caused by refrigerant in the container,

spacing member 44 will also contract an equal overall amount. This willforce the rod 30 toward window 40 and thus maintain distance between 32and window 40 substantially constant. When sapphire is used for rod 30,spacing member 44 is preferably constructed from phenol-formaldehyderesins reinforced with fabric or paper. The other end of inner vessel 12is supported by the tubes 20 and 22 forming the bottom filling tube.

An alternate form of the invention which is useful for containersemploying a different apparatus for mounting the infra-red detectioncell is shown in FIG. 2. In this embodiment the cell 32 is mountedagainst the inner wall of a hollow extension 50 in the bottom of innervessel 12 into which liquid refrigerant passes. Still another form ofthe invention is shown in FIG. 3 whereby the filling and vent meansenter from the side of the container. In this modification the problemof liquid refrigerant flowing out through the vent annular passage issubstantially eliminated.

Similar reference numerals have been used in all of the figures todenote similar parts for the sake of clarity.

In some missile configurations bottom filling of the refrigerationcontainer is highly desirable. The present invention, especially in theform shown by FIGS. 1 and 2, is believed to be the only system presentlyknown that can be conveniently used in such bottom-filling situations.

A device of the type shown in FIG. 1 having an over all length of about5 inches and about 2 /2 inches wide successfully maintained desiredoperating temperature at the infra-red detection cell for 6 to 7 hourswithout refilling. This provides adequate operating life for aninfra-red detection cell cooling system on a missile. Tube 22 Was about-inch CD. with 0.006 in. wall thickness and tube 20 was about /s-inch.0D. with 0.010 in. wall thickness. These small tubes in combination withfill line 26 having a maximum 0.1). of about Az-inch provided a path ofhigh resistance to heat inleak.

The term vacuum as used herein is intended to apply to subatmosphericpressure conditions not substan tially greater than 1000 microns ofmercury, and preferably below 100 microns of mercury absolute. The termopacified insulation as used herein refers to a twocomponent insulatingsystem comprising a low heat conductive, radiation'permeable materialsuch as silica or fiber glass and a radiant heat impervious materialsuch as copper or aluminum flakes or foil which is capable of reducingthe passage of infra-red radiation rays without significantly increasingthe thermal conductivity of the insulating system.

Adsorbent 18, either in powder or pellet form, is preferably used in theinsulation jacket to remove by adsorption any gas which may leak intothe jacket space. This is important since no provision is made in theserelatively small storage containers for re-evacuation of the insulatingjacket. In particular, zeolitic molecular sieves having pores of atleast about 5 Angstrom units in size, are preferred as the adsorbentsince they have extremely high adsorptive capacity at the temperatureand pressure conditions existing in the insulating "jacket and arechemically inert toward any gases which might leak into the insulatingjacket. However, other adsorbents such as silica gel, activated aluminaand activated charcoal may also be used if so desired. Alternativelyactive metal getters that function by chemically combining withinleaking and residual air may be used.

As may be seen from the above description and example the refrigeratedinfra-red detection cellmounting means of the present invention givesvery satisfactory results in terms of thermal efficiency and operatinglife for a given charge of refrigerant. While certain preferredembodiments of the invention have been shown and described it is to beunderstood that certain modifications could be made by a person skilledin the art without departing from the spirit and scope thereof;

What is claimed is: g

1. Apparatus comprising an inner liquefied-gas storage vessel; an outerprotective shell surrounding the vessel and spaced therefrom to form anevacuable insulation space therebetween; inner vessel refrigerantfilling and venting means extending into the apparatus and terminatingadjacent an inner surface of said vessel within the normal vapor spacethereof, such means comprising a double-walled conduit; an elongatedoutwardly-extending member appended to the outer shell and constructedand arranged such that a small object may be positioned Within the outerend thereof; and elongated heattransfer means positioned within themember and spaced from the Walls thereof for refrigerating such objectwhereby sensible heat is conducted from said object to the refrigerantin said vessel.

2. Apparatus according to claim 1 wherein the member depends from saidouter shell; and wherein the interior of said heat transfer means is inliquid communication with the interior of said vessel and comprisesliquefied gas in thermal contact with said object.

3. Apparatus according to claim 1 wherein said elongated heat transfermeans comprises a solid rod of thermally conductive material in thermalcontact with said object and said vessel.

4. Apparatus according to claim 3 wherein said object is an infra-reddetecting cell which is affixed to the outer end of the rod; and whereinan infra-red radiation transparent window is positioned in the end ofsaid member adjacent said object; and wherein at least the innerlongitudinal portion of said member comprises a material havingsubstantially the same overall coefiicient of thermal contraction assaid rod, such inner portion being so constructed and arranged tomaintain said object in substantial alignment with the adjacent windowwhen in operation.

5. Apparatus according to claim 1 wherein said member and said heattransfer means comprise two spaced concentric outwardly-extendingconduits gas-tightly connected to said outer shell and vesselrespectively, and are constructed and arranged such that the spacebetween such concentric extended conduits is in gaseous communicationwith said evacuable insulation space; and wherein said object ispositioned within said space.

6. Apparatus according to claim 1 wherein the vessel filling and ventingmeans comprises two spaced concentric 'nwardiyextending conduitsgas-tightly connected to said outer shell and vessel, respeclively, andis constructed and arranged such that the space between such concentricextended conduits is in gaseous communication with said evacuableinsulation space; and wherein the interior of such means is adapted toreceive an insertable liquid filling conduit of a size such that anannular vapor vent passage is provided between the interior of suchmeans and the liquid filling conduit.

7. Apparatus comprising an inner liquefied gas storage vessel; an outerprotective shell surrounding the vessel and spaced therefrom to form anevacuable insulation space therebetween; inner vessel filling andventing means extending into the apparatus and terminating adjacent aninner surface of said vessel within the normal vapor space thereof, suchmeans comprising two spaced concentric inwardly-extending conduitsgas-tightly connected to said outer shell and vessel, respectively,which are constructed and arranged such that the space between suchconcentric extended conduits is in gaseous communication with saidevacuable insulation space, the interior of such means being adapted toreceive an insertable liquid filling conduit of a size such that anannular vapor vent passage is provided between the interior of suchmeans and the liquid filling conduit; an elongated outwardly-extendingmember comprising two spaced concentric conduits gas tightly connectedto said outer shell and vessel, respectively, such member beingconstructed and arranged such that the space between the concentricconduits provides gas communication with said evacuable insulationspace, and such member being further constructed and arranged such thatan infra-red detecting cell may be positioned Within the outer end ofsaid space; an infra-red radiation transparent window positioned in theend of said member adjacent said infra-red detecting cell; and heattransfer means positioned within said member for refrigerating saidinfra-red detecting cell whereby sensible heat is conducted from thecell into said vessel.

8. Apparatus comprising an inner liquefied-gas storage vessel; an outerprotective shell surrounding the vessel and spaced therefrom to form anevacuable insulation space therebetween; inner vessel filling andventing means; an elongated outwardly-extending member appended to theouter shell and constructed and arranged such that an infra-reddetecting cell may be positioned within the outer end thereof; aninfra-red radiation transparent Window positioned in the end of suchmember adjacent said infra-red detecting cell; an elongated rod composedof thermally conductive material positioned within said memher andspaced from the walls thereof for refrigerating said infra-red detectingcell whereby sensible heat is conducted from said infra-red detectingcell to the refrigerant in said vessel; and a material havingsubstantially the same overall coeflicient of thermal contraction assaid rod comprising at least the inner longitudinal portion of saidmember, such inner portion being so constructed and arranged to maintainsaid infra-red detecting cell in substantial alignment with the adjacentwindow when in operation.

9. Apparatus according to claim 8 wherein said rod is constructed ofsapphire and said material comprising the inner longitudinal portion ofsaid member is constructed of a reinforced phenol-formaldehyde resin.

References Cited in the file of this patent UNITED STATES PATENTS2,593,916 Pefi Apr. 22, 1952 2,671,154 Burstein Mar. 2, 1954 2,677,245Edmondson May 4, 1954 2,794,560 Johnson Mar. 12, 1957 2,816,232 BursteinDec. 10, 1957 2,953,529 Schultz Sept. 20, 1960 OTHER REFERENCES Advancesin Cryogenic Enigneering, volume 4, Proceedings of the 1958 CryogenicConference, Cambridge, Mass. September 3-8, 1958, Plenum Press, 1960,pages 426 to 435.

